This invention relates to electromechanical contactors.
Contactors frequently utilize a longitudinal moveable carrier having a moveable armature at one end and spring mounted moveable contacts, e.g. contact bridges, at the other. The contact carrier extends through an insulating member, e.g. arc chute, and its armature is resiliently displaced from the stationary electromagnet. The moveable and stationary contacts, the armature, stationary magnet and operating coil may be retained within the combination of the arc chute and of a base plate. However, such assemblies are often subject to undesirable tolerance variations.
One critical dimension relates to the travel of the armature and moveable contact carrier. With the stationary electromagnet deenergized, the contact carrier and armature are positioned so that the moveable contacts are displaced from the stationary contacts. Upon energization of the electromagnet and attraction of the armature, the contact carrier moves from its normal position to the final position where the armature abuts the pole faces of the stationary magnet. After partial movement, the moveable contact initially abuts the stationary contacts. This position is referred to as the kiss position. During further movement, the moveable and stationary contacts remain in contact with additional spring, i.e. contact, pressure being applied. The distance between the kiss position and the final position is termed "wipe", "wear allowance" or "overtravel allowance". One critical parameter is the distance the pole faces of the stationary magnet are displaced from the armature when the contact carrier is in the kiss position. If this distance is too small, i.e. insufficient wipe, there is insufficient assurance that the moveable and stationary contacts will close with sufficient contact pressure. Also after some contact wear the contacts do not close properly, resulting in insufficient contactor life. The wipe distance must be sufficiently great to assure proper closure despite tolerance variations or normal contact wear. If the distance between the kiss and final positions is too great, the magnet may not exert sufficient pull to reliably close the contacts. This excessive distance could also prevent the armature from abutting the pole faces of the stationary magnet. This can cause excessive currents in, and thus burn out, the operating coil.
The critical positioning of the stationary magnet may not be obtained because of tolerance variations in a plurality of contactor components. These contributing components generally include the armature, moveable contact carrier, moveable and stationary contacts, stationary magnet arc chute and base place. The sum of these tolerances, i.e. the tolerance build up, is frequently excessive. Oversize electromagnets can be used to insure contact closure. However, this results in increased size, magnet costs and operating cost. However, contactors must nevertheless be tested to determine whether they have an acceptable tolerance range, and nonacceptable devices must be scrapped or reworked.
Contactors energized by alternating current commonly use laminated stationary magnets to reduce eddy currents. Shading coils are frequently mounted on the magnet legs. The shading coils, also called pole shaders, constitute a single closed turn of proper resistance to enhance the sealing pull upon closure of the armature on the pole faces of the magnet legs. These pole shaders are frequently secured to the magnet leg, e.g. by crimping or cementing.